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Trucking Trout to Their Native Streams

Fish and Wildlife ServiceBull trout are genetically adapted to the habitat of particular streams.

In an innovative conservation effort, biologists on the Clark Fork River are using genetic testing to help get bull trout back to their natal streams to spawn.

Fulfilling a requirement for the relicensing of its two hydroelectric power plants on the river in Idaho and Montana, Avista Utilities is having the fin tissue of randomly caught adult bull trout “fingerprinted.” Juvenile fish in the natal streams are also sampled to determine whether they carry the DNA of the adults.

The fish are caught by hook and line, or by electrofishing, a process that involves sending a mild electric current through the water to temporarily immobilize fish so they can be captured. A tiny fin portion is then clipped and sent to a Fish and Wildlife Service laboratory in Washington State.

The trout are held in a circular tank until a genetic analysis determines which stream they were “imprinted” to at birth, and then they are trucked to the appropriate destination, said Joe DosSantos, a fisheries biologist with Avista.

The goal of the project is to protect the genetic integrity of the trout and thereby increase their numbers on Clark Fork, where fewer than 200 of the native salmonids run each fall as a result of the effect of mineral mining, dewatering and the construction of dams.
“The whole idea is to geographically put the population back together the way it was before the system got fragmented,” Mr. DosSantos said.

Bull trout are genetically adapted to the habitat of certain streams, said Wade Fredenberg, a fisheries biologist with the federal Fish and Wildlife Service, a partner in the project.

“If they can’t get to where they need to go, they’ll settle, but they may go into drainages where water temperature, sediment and other issues make the eggs not so viable,” he said. “We have to get them above the dams, and the right dam, too.”

Avista’s hydroelectric dams, the Cabinet Gorge dam near Clark Fork, Idaho, and the Noxon Rapids dam about 20 miles upstream near Noxon, Mont., were built about 60 years ago.

The genetic assignment project focuses on seven of more than 30 tributaries above the two dams, each with discrete spawning populations of bull trout. About 50 adult fish, or roughly 40 percent of the total run up Clark Fork from Lake Pend Oreille, are captured and transferred each year at an annual cost of $250,000. That comes to about $5,000 a trout.

Biologists with the project say it is a small price to pay to restore one of the Columbia River Basin’s most culturally significant species.

“We’re trying to boost numbers, and it’s happening,” Mr. Fredenberg said. “On Graves Creek, we captured every fish that went up and we looked at juveniles going back to Pend Orielle, and we could tell who their parents were. These were fish we had transferred above the Cabinet Gorge dam, so it’s verification they’re fulfilling the life cycle.”

Although the project would not be possible without scientific advances that allow workers to decipher DNA in less than 48 hours, it is also labor intensive. Bull trout reproduce in late fall by digging redds, or nests, with their tails, and then depositing eggs. It can take five months for the eggs to develop and hatch in the coldest temperatures of the year.

“Besides having a high affinity for a particular tributary, they have a high affinity to a particular spawning area in the trib, typically one where an underwater spring is keeping water oxygenated and the spawning gravel clean,” Mr. DosSantos said. “These areas of upwelling are their ace in the hole, and they want to return to them every year.”

Results over the last three years indicate that the percentage of juveniles carrying the transported adults’ genes has ranged from 20 percent to 60 percent, Mr. DosSantos said.

“We may look at 200 juveniles a year, less than 10 percent of a stream’s population, but it is a representative sample,” he said. “We’re seeing that if we get the adults back to where they want to go, they’ll contribute to the juvenile population.”

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